Method and apparatus for leak detection in blood circuits combining external fluid detection and air infiltration detection

ABSTRACT

One of the most significant safety concerns in the automation of extracorporeal blood treatments such as dialysis is the risk of blood leakage. Extracorporeal blood treatment systems draw blood at such a high rate that a loss of integrity in the blood circuit can be catastrophic. There are a number of mechanisms for detecting and preventing leaks, but none is perfect. According to the present invention, the probability of a leak, its seriousness, the amount of time the leak condition has persisted without a response, and other factors may be used to control escalation of multiple types of alarms. In a simple embodiment, for example, there may be a staged audio signal that has a certain loudness and tonal quality when a leak is first detected and becomes more conspicuous as time goes by without a reset response from a user.

FIELD OF THE INVENTION

[0001] The present invention relates to the detection of a leak(including needle-disconnects and other causes of loss of integrity) inextracorporeal blood circuits and more particularly to the use of acombination of the detection of air and blood escaping from the bloodcircuit to increase responsiveness, sensitivity, and reliability ofdetection of leaks.

BACKGROUND

[0002] Many medical procedures involve the extraction and replacement offlowing blood from, and back into, a donor or patient. The reasons fordoing this vary, but generally, they involve subjecting the blood tosome process that cannot be carried out inside the body. When the bloodis outside the patient it is conducted through machinery that processesthe blood. The various processes include, but are not limited to,hemodialysis, hemofiltration, hemodiafiltration, blood and bloodcomponent collection, plasmaphresis, aphresis, and blood oxygenation.

[0003] One technique for extracorporeal blood processing employs asingle “access,” for example a single needle in the vein of the patientor a fistula. A volume of blood is cyclically drawn through the accessat one time, processed, and then returned through the same access atanother time. Single access systems are uncommon because they limit therate of processing to half the capacity permitted by the access. As aresult, two-access systems, in which blood is drawn from a first access,called an arterial access, and returned through a second access, calleda venous access, are much faster and more common. These accesses includecatheters, catheters with subcutaneous ports, fistulas, and grafts.

[0004] The processes listed above, and others, often involve themovement of large amounts of blood at a very high rate. For example, 500ml. of blood may be drawn out and replaced every minute, which is about5% of the patient's entire supply. If a leak occurs in such a system,the patient could be drained of enough blood in a few minutes to causeloss of consciousness with death following soon thereafter. As a result,such extracorporeal blood circuits are normally used in very safeenvironments, such as hospitals and treatment centers, and attended byhighly trained technicians and doctors nearby. Even with closesupervision, a number of deaths occur in the United States every yeardue to undue blood loss from leaks.

[0005] Leaks present a very real risk. Leaks can occur for variousreasons, among them: extraction of a needle, disconnection of a luer,poor manufacture of components, cuts in tubing, and leaks in a catheter.However, in terms of current technology, the most reliable solution tothis risk, that of direct and constant trained supervision in a safeenvironment, has an enormous negative impact on the lifestyles ofpatients who require frequent treatment and on labor requirements of theinstitutions performing such therapies. Thus, there is a perennial needin the art for ultra-safe systems that can be used in a non-clinicalsetting and/or without the need for highly trained and expensive staff.Currently, there is great interest in ways of providing systems forpatients to use at home. One of the risks for such systems is the dangerof leaks. As a result, a number of companies have dedicated resources tothe solution of the problem of leak detection.

[0006] In single-access systems, loss of blood through the patientaccess and blood circuit can be indirectly detected by detecting theinfiltration of air during the draw cycle. Air is typically detectedusing an ultrasonic air detector on the tubing line, which detects airbubbles in the blood. The detection of air bubbles triggers the systemto halt the pump and clamp the line to prevent air bubbles from beinginjected into the patient. Examples of such systems are described inU.S. Pat. Nos. 3,985,134, 4,614,590, and 5,120,303.

[0007] While detection of air infiltration is a reliable technique fordetecting leaks in single access systems, the more attractive two-accesssystems, in which blood is drawn continuously from one access andreturned continuously through another, present problems. While adisconnection or leak in the draw line can be sensed by detecting airinfiltration, just as with the single needle system, a leak in thereturn line cannot be so detected. This problem has been addressed in anumber of different ways, some of which are generally accepted in theindustry.

[0008] The first level of protection against return line blood loss isthe use of locking luers on all connections, as described inInternational Standard ISO 594-2 which help to minimize the possibilityof spontaneous disconnection during treatment. Care in the connectionand taping of lines to the patient's bodies is also a known strategy forminimizing this risk.

[0009] A higher level of protection is the provision of venous pressuremonitoring, which detects a precipitous decrease in the venous linepressure. This technique is outlined in International Standard IEC60601-2-16. This approach, although providing some additionalprotection, is not very robust, because most of the pressure loss in thevenous line is in the needle used to access the patient. There is verylittle pressure change in the venous return line that can be detected inthe event of a disconnection, so long as the needle remains attached tothe return line. Thus, the pressure signal is very weak. The signal isno stronger for small leaks in the return line, where the pressurechanges are too small to be detected with any reliability. One way tocompensate for the low pressure signal is to make the system moresensitive, as described in U.S. Pat. No. 6,221,040, but this strategycan cause many false positives. It is inevitable that the sensitivity ofthe system will have to be traded against the burden of monitoring falsealarms. Inevitably this leads to compromises in safety. In addition,pressure sensing methods cannot be used at all for detecting smallleaks.

[0010] Yet another approach, described for example in PCT applicationUS98/19266, is to place fluid detectors near the patient's access and/oron the floor under the patient. The system responds only after blood hasleaked and collected in the vicinity of a fluid detector. A misplaceddetector can defeat such a system and the path of a leak cannot bereliably predicted. For instance, a rivulet of blood may adhere to thepatient's body and transfer blood to points remote from the detector.Even efforts to avoid this situation can be defeated by movement of thepatient, deliberate or inadvertent (e.g., the unconscious movement of asleeping patient).

[0011] Still another device for detecting leaks is described in U.S.Pat. No. 6,044,691. According to the description, the circuit is checkedfor leaks prior to the treatment operation. For example, a heated fluidmay be run through the circuit and its leakage detected by means of athermistor. The weakness of this approach is immediately apparent: thereis no assurance that the system's integrity will persist, throughout thetreatment cycle, as confirmed by the pre-treatment test. Thus, thismethod also fails to address the entire risk.

[0012] Yet another device for checking for leaks in return lines isdescribed in U.S. Pat. No. 6,090,048. In the disclosed system, apressure signal is sensed at the access and used to infer its integrity.The pressure wave may be the patient's pulse or it may be artificiallygenerated by the pump. This approach cannot detect small leaks and isnot very sensitive unless powerful pressure waves are used; in whichcase the effect can produce considerable discomfort in the patient.

[0013] Clearly detection of leaks by prior art methods fails to reducethe risk of dangerous blood loss to an acceptable level. In general, therisk of leakage-related deaths increases with the decrease in medicalstaff per patient driven by the high cost of trained staff. Currently,with lower staffing levels comes the increased risk of unattended leaks.Thus, there has been, and continues to be, a need in the prior art for afoolproof approach to detection of a return line leak or disconnection.

SUMMARY OF THE INVENTION

[0014] According to the present invention, leak detection sensitivityand reliability of leak detection are enhanced by combining thedetection of fluid leaking from protected blood circuit with detectionof air infiltration into the blood circuit. The latter is a newtechnique described in the commonly assigned pending application “Methodand Apparatus for Leak Detection in a Fluid Line,” the entirety of whichis hereby incorporated by reference as if fully set forth herein in itsentirety. The new method identifies leaks in a normally positivepressure part of a circuit where infiltration does not ordinarily resultfrom a leak. The portion that is ordinarily under negative pressureexperiences infiltration which may be detected by an air sensor in ablood processing machine. A fluid detector is located within the bloodprocessing machine and detects any leakage from within the housing ofthe blood processing machine. The lines extending outside the bloodprocessing machine are protected by the detection of leaks by detectingair infiltration in accord with the method and apparatus described inthe application incorporated by reference above.

[0015] In an embodiment of the invention, a funnel is incorporated inthe blood processing machine to guide and concentrate any blood leakingfrom the circuit into a fluid detector. The fluid detector may be acontinuity sensor relying on electrolyte conduction to sense fluid, atemperature sensor, a pH sensor, an impact sensor detecting drops, orany other sensor effective to detect blood leaking out of the circuit.

[0016] Another embodiment allows retrofit to an existing bloodprocessing machine. This embodiment may include a funnel added to thebottom to collect any blood leaking from it. The funnel may be aflexible bag-like component that can be attached with hook and loop-typeconnectors to the bottom of the blood processing machine. If a retrofitembodiment of the leak detection device of the application incorporatedby reference above is used with a conventional blood processing machine,the retrofit funnel may be made large enough to cover both the bloodprocessing machine, the retrofit leak detector device, and theconnecting tubing.

[0017] The invention will be described in connection with certainpreferred embodiments, with reference to the following illustrativefigures so that it may be more fully understood. With reference to thefigures, it is stressed that the particulars shown are by way of exampleand for purposes of illustrative discussion of the preferred embodimentsof the present invention only, and are presented in the cause ofproviding what is believed to be the most useful and readily understooddescription of the principles and conceptual aspects of the invention.In this regard, no attempt is made to show structural details of theinvention in more detail than is necessary for a fundamentalunderstanding of the invention, the description taken with the drawingsmaking apparent to those skilled in the art how the several forms of theinvention may be embodied in practice.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is an illustration of a blood processing machine with leakdetection built into it including a fluid sensor to detect blood outsidethe blood circuit and one or more air sensors for detecting theinfiltration of air into the blood circuit due to a leak.

[0019]FIG. 2 is an illustration of a retrofit configuration thatprovides the functionality of the device of FIG. 1 for a conventionalblood processing machine without leak detection, the illustrationshowing connected to the conventional blood processing machine, aretrofit device providing air-detection and a retrofit funnel and fluidsensor to detect blood outside the blood circuit.

[0020]FIG. 3 is a block diagram of a control system consistent withvarious embodiments of the invention.

[0021]FIG. 4 is a figurative diagram of a retrofit configuration havinga conventional blood processing machine and a leak detection portioncombining both fluid detection and air infiltration detection to providefull coverage of a blood circuit.

[0022]FIG. 5 is an illustration of a fluid-detecting transponderaccording to another embodiment of the invention.

[0023]FIG. 6 is an illustration of a leak detection embodiment makinguse of the transponder of FIG. 5.

[0024]FIG. 7 is an illustration of an acoustic network for connectingcomponents of various embodiments of the current invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] Referring now to FIG. 1, a blood processing machine 146 fortreating a patient 110 has leak detection components built into it. Themachine includes air sensors 160 and 170, a filter 180, and a reversiblepump 175, the latter being one mechanism for reversing flow to test thereturn circuit as discussed in the patent application incorporated byreference above.

[0026] During operation, the pump 175 reverses periodically to test thenormally high-pressure side 162 of the circuit. When the pump 175reverses, a negative pressure is generated on the normally high-pressureside 162 of the circuit that will draw air into any leaks. The air willthen be detected by air sensor 160. During forward operation, the airsensor 170 detects any leaks because air will infiltrate the normallylow-pressure side 163 of the circuit. Thus, the two air sensors 160 and170 quickly detect any leaks in when the pump is driven in forward andreverse directions, respectively.

[0027] Within a housing 181, a funnel 190 directs any blood leaking fromthe housed portion 184 of the circuit toward a fluid detector 185. Anyleaks occurring in the housed portion 184 will be directed by the funnel190 toward the fluid detector 185. The fluid detector 185 may be anysuitable device for detecting blood, for example, a continuity testerresponsive to electrolytic conduction, a temperature sensor, a pHsensor, an impact sensor detecting drops, or any other sensor effectiveto detect blood leaking out of the circuit 184.

[0028] The fluid detector 185 may be linked to the same alarm system asthe air sensors 160 and 170. The system may be programmed such that theair sensors 160 and 170 “protect” the access lines 162 and 163 outsidethe machine by providing for flow reversal only as far as necessary todetect leaks in normally-positively pressurized lines. In that case, thefluid detector 185 may provide warning for any leaks inside the bloodprocessing machine 146 and the air sensors 160 and 170 protection forthe access lines.

[0029] Alternatively, the system may be programmed such that theprotection fields overlap, that is, the pump 175 reverses for asufficient displacement of blood that any leaks at all may be detectedwhile air detection provides another level of protection. In this case,if the sensitivity of the air detector 160 and 170-based leak detectionis raised, but modulated according to the status of the fluid detector165 signal such that an air sensor signal of a low level indicating aleak does not result in an alarm condition unless it is accompanied by aleak indication by the fluid detector 165, false positives arising fromthe air sensors can be reduced and the sensitivity of the systemenhanced. The sensitivity of the fluid detector may be similarlyincreased, resulting in the possibility of detecting smaller leaks thana system calibrated to operate without such “cooperation” among leakdetection subsystems. Note that the overlap in protection zones can beincreased by providing one or more additional fluid detectors under thelines or an extension to the funnel 190 to catch fluid leaking from theaccess lines 162 and 163.

[0030] Note that the configuration of FIG. 1 need not have two airsensors as should be clear from the application incorporated byreference. A single air sensor can serve as a detector of infiltrationin both lines.

[0031] Referring now to FIG. 3, air or infiltration sensors 330 and oneor more fluid sensors 335 are connected to send signals to a controller300. The controller 300, in turn, controls alarms 1-N 320 . . . 325, thepump 305, a flow controller such as four-way valve (See FIG. 2 andattending discussion) and line clamps 315. To stop any loss of blood,the lines of the blood circuit may be clamped by one or more line clamps315 and the pump 305 shut down. The controller 300 may be a programmableprocessor, a simple relay network, or any other suitable type of controldevice.

[0032] The logic of the control algorithm may be a simple invocation ofa shut-down and alarm procedure when a signal from either the air orinfiltration sensor(s) 330 or the fluid sensor(s) 335 goes beyond athreshold. The shut-down and alarm procedure may be one known in theprior art or any other suitable process up to the discretion of thesystem designer.

[0033] Referring now to FIG. 2, in an alternative design that issuitable for retrofit to a conventional blood processing machine 246. Aseparate leak detection device 248 periodically reverses flow throughthe patient side of the blood circuit 267 so that a negative pressure isgenerated in a normally positive pressure side 262 of the blood circuit.The leak detection device does this by switching a four-way valve 205 astaught in the application incorporated by reference above. The airsensors 160 and 170 serve the same purpose as in the embodiment ofFIG. 1. That is, air will infiltrate either line, normal-return 262 ornormal draw 263, at some point when the flow is in a correspondingdirection. The air infiltration, and thereby the leak, will ultimatelybe detected by one of the air sensors 160 and 170.

[0034] Any blood leaking from any part of the blood processing machine246, the leak detecting device 248, or the connecting portions of thecircuit 279 are collected by a retrofit funnel attachment 210 anddirected to a fluid sensor 212 therein. The retrofit funnel 210 may be asimple flexible bag-like structure or a rigid structure. The latter maypermit a one-size-fits-all product that can be adapted to any size bloodprocessing machine 246 and leak detection device 248. The funnel 210 maybe attached using any suitable fasteners 220 such as hook and loop orbolt-on fasteners.

[0035] Referring to FIG. 4, the leak detection device may have a housingfunnel 316 with a fluid detector 314 built into it. In this case, aretrofit funnel 310 and fluid detector 312 need only be attached to theblood processing machine and adapted to catch any leaks from theconnecting lines 279 as illustrated. The funnel 310 may be attached byany suitable means such as by hook and loop fasteners 315. Again thefunnel 310 may be made of flexible plastic to permit it to be fit aroundobstacles or differently-size machines.

[0036] Referring now to FIG. 5, a fluid detecting transponder 390detects fluid and emits a wireless signal in response to the detection.The transponder has a fluid sensor portion 385 and a transmitter portion375. The transponder has a power source (not shown) such as a battery.The transmitter portion 375 may emit a radio or acoustic signal.Referring now also to FIG. 6, one or more transponders 390 may be placedinside the housing of a blood processing machine 246 as illustrated at395. Alternatively, in systems where the blood circuit is mounted to apanel and exposed, the transponders 390 may be placed below the bloodprocessing machine in a trough or other open container 396 asillustrated at 397.

[0037] Referring now to FIG. 7, a multiple-input/multiple-level leakdetection system may employ multiple sensors, such as in the embodimentof FIG. 6. The many sensors are indicated at 405, 410, . . . 415 tocommunicate with a controller 420 and for the controller 420 tocommunicate with multiple output devices and user interfaces 424 anddata processors and relays 422. In the present embodiment, rather thanwire the components together, they communicate with each other usingrespective sound signal generators 425, 426, 427, 428, 429, and 423 andreceivers 431, 432, 433, and 434, for example, as in the transducer 390of FIG. 5.

[0038] The signals are preferably articulated sufficiently to encodeunique identifiers so that multiple systems within “hearing” range ofone another do not cause interference. Also, the sound pattern mayencode information other than an identifier of the transmitter and/orreceiver, for example, it can encode a type of status or magnitude of adetected condition, such as heart rate or degree of wetting of a fluiddetector. The sounds may be above or below the frequency range of humanhearing to avoid the subjective impact. Alternatively, the signals maybe spread over ranges of frequency by modulating with a pseudorandomcode. The subject effect of such spread-spectrum signals can be very lowdue to the noise-like nature of the sound and the low power levelsrequired for data transmission.

[0039] In a system where the components of a multiple input alarm systemmay only need to communicate with each when conditions reach an abnormalstatus, the audibility of a given signal may pose a problem. Theparticular alarm system application, therefore, may provide aninoffensive context for using acoustic signals to communicate betweencomponents; a sort of “chirp network” to interconnect the functionalcomponents of the system. In fact, the audibility of communicationsignals may provide a benefit. For example, an attendant called to alocation by a remote-station alarm may be greeted not only by a userinterface indicating the nature of the problem but also by the sendingunit's characteristic audio signal. This may reinforce the output fromthe user interface increasing comprehension by the attendant of thealarm condition that occurred.

[0040] Some sensors, such as indicated for sensor C 415, may have theability to receive as well as send signals. The data processor/relay 422may be, for example, a component of the acoustic network that processesinformation outside the controller 420. For example, it could reducedata from other sources unburdening the controller 420 or permittingfeature-upgrades to the controller without requiring its replacement ormodification.

[0041] Although the invention has been described in connection with ablood circuit having simply a pump and a filter, such as a dialysis orhemofiltration system, this type of circuit was only used as an examplefor purposes of discussion. It should be clear from the disclosure thatthe invention is applicable to any kind of blood processing system,including hemodiafiltration, blood and blood component collection,plasmaphresis, aphresis, blood oxygenation, blood factor (e.g., stemcell) harvesting and all manner of extracorporeal blood processing. Theinvention is also applicable to infusion systems as should be clear fromthe current specification, particularly in combination with theteachings of the application incorporated by reference above.

[0042] It will be evident to those skilled in the art that the inventionis not limited to the details of the foregoing illustrative embodiments,and that the present invention may be embodied in other specific formswithout departing from the spirit or essential attributes thereof. Thepresent embodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription, and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

What is claimed is:
 1. A method of detecting leaks in an extracorporealblood circuit, comprising the steps of: detecting fluid outside a firstportion of a blood circuit; detecting air inside a second portion of ablood circuit located remote from said first portion such that fluid isnot detectable from said second portion; generating an alarm signalresponsively to a result of either or both of said steps of detecting.2. A method as in claim 1, wherein said first step of detecting includesproviding a fluid sensor below said circuit first portion and sensing apresence of blood with said sensor.
 3. A method as in claim 1, whereinsaid second step of detecting includes applying a positive gaugepressure to said circuit during a first time and applying a negativepressure to said blood circuit during a second time.
 4. A method as inclaim 1, wherein said step of generating includes generating an alarm ifeither of said first and second steps of detecting results in anindication of a leak.
 5. A method as in claim 1, wherein said secondstep of detecting includes periodically reversing a flow in said bloodcircuit.
 6. A method as in claim 1, wherein said second step ofdetecting includes positioning a funnel with a fluid detector under ablood processing machine.
 7. A method as in claim 1, wherein said secondportion includes tubing linking a patient to a blood processing machine.8. A method as in claim 7, wherein said first portion includes a portionof said blood circuit at least partially housed by a blood processingmachine.
 9. A method as in claim 8, wherein said step of detecting fluidincludes directing a flow of fluid by gravity by means of a funnel to afluid detector.
 10. A leak detection system for an extracorporeal bloodcircuit, comprising: a fluid detector located in a position to captureleaking blood from a first portion of said blood circuit; a mechanism insaid blood circuit to, at least periodically, create a negative pressurein all portions of a patient side of said blood circuit such that anyleaks in said all portions will result in infiltration of air; an airinfiltration detector located to detect air infiltrating said secondportion; an alarm connected to both said air infiltration detector andsaid fluid detector and configured to generate an alarm signal if eithersaid air infiltration detector or said fluid detector indicates a leak.11. A device as in claim 10, further comprising a container positionedwith respect to said fluid detector to guide blood leaking from saidblood circuit toward said fluid detector.
 12. A device as in claim 10,wherein said mechanism includes a device adapted to reverse flow in saidblood circuit.
 13. A device as in claim 12, wherein said device adaptedto reverse flow includes a reversing valve.
 14. A device as in claim 13,further comprising a funnel-shaped container positioned with respect tosaid fluid detector to guide blood leaking from said blood circuittoward said fluid detector located at a bottom of said container.
 15. Adevice as in claim 14, wherein said funnel-shaped container is builtinto a housing of a blood processing machine of which said blood circuitis a part.
 16. A device as in claim 10, wherein said air infiltrationdetector is a detector of the presence of air in said blood circuit. 17.A device for detecting leaks in a blood circuit, comprising: a firstleak detector that detects leaks by sensing blood outside said bloodcircuit, said first leak detector being located to detect leaks from afirst portion of said blood circuit located remote from a patient; asecond leak detector that detects leaks by sensing air infiltration intolines under negative pressure; said second leak detector beingconfigured to detect leaks in lines connecting said patient to saidfirst portion; a mechanism that insures that at least part of said linesare under negative pressure at least part of the time during a treatmentsuch that a detectable air infiltration indicates a presence of a leakin said lines; an alarm device that outputs an alarm signal responsivelyto a detection of a leak by said first or second leak detector.
 18. Adevice as in claim 17, wherein said second leak detector includes afluid sensor below said circuit first portion.
 19. A device as in claim17, wherein said mechanism includes a flow-reversing valve in said bloodcircuit effective to reverse flow in said lines.
 20. A device as inclaim 17, where in said first leak detector is located below said firstportion, said device further comprising a flow director to concentrateleaking fluid toward said first leak detector.
 21. A method of detectinga fluid leak from a fluid processing machine, comprising the steps of:detecting infiltration of air into a fluid circuit; detecting leakage offluid from said fluid circuit; generating an alarm responsively to saidfirst and second steps of detecting.
 22. A method as in claim 21,wherein said step of generating includes generating an alarm when eitherof said steps of detecting indicates a leak.
 23. A method as in claim21, wherein said first step of detecting is restricted to detectinginfiltration into a first part of said fluid circuit and said secondstep of detecting is restricted to detecting fluid leaking from a secondpart of said fluid circuit, said first and second parts having separaterespective portions.
 24. A method as in claim 21, wherein said firststep of detecting includes generating a negative pressure in said fluidcircuit.
 25. A method as in claim 25, wherein said step of generatingincludes reversing a flow of fluid.
 26. A method as in claim 21, whereinsaid fluid is blood.
 27. A method as in claim 21, wherein said fluidprocessing machine is an extracorporeal blood processing machine.
 28. Amethod of detecting a leak from a blood circuit of an extracorporealblood treatment machine, comprising the steps of: detecting leakage ofblood from respective portions of a blood circuit; said step ofdetecting including detecting different physical effects resulting fromrespective conditions associated with one or more leaks; said respectiveportions including parts that are non-overlapping.
 29. A method as inclaim 28, wherein said step of detecting includes triggering anindicator of a leak responsively to a result of either of saidrespective different physical effects.
 30. A method as in claim 29,further comprising at least one of clamping a fluid line, stopping apump, or actuating a flow controller responsively to said indicator. 31.A method as in claim 29, further comprising triggering an alarmresponsively to said indicator.
 32. A method as in claim 28, whereinsaid different physical effects include the infiltration of air into ablood circuit and the presence of blood outside said blood circuit. 33.A method as in claim 32, further comprising controlling an output deviceresponsively to said indicator.
 34. A method as in claim 32, furthercomprising at least one of clamping a fluid line, stopping a pump, oractuating a flow controller responsively to said indicator.
 35. A methodas in claim 32, further comprising outputting an alarm signalresponsively to said indicator.
 36. A method as in claim 35, whereinsaid step of detecting includes triggering an indicator of a leakresponsively to a result of either of said respective different physicaleffects.
 37. A method as in claim 36, wherein said different physicaleffects include the infiltration of air into a blood circuit and thepresence of blood outside said blood circuit.
 38. A method as in claim28, wherein said different physical effects include the infiltration ofair into a blood circuit by periodically generating a negative pressurein said blood circuit and the presence of blood outside said bloodcircuit.
 39. A method as in claim 38, wherein said step of generatingincludes reversing a flow of blood.
 40. A method as in claim 28, whereinsaid different physical effects include the infiltration of air into ablood circuit by periodically reversing a flow of blood in said bloodcircuit using a reversing valve and the presence of blood outside saidblood circuit.
 41. A method as in claim 40, wherein said presence isdetected using a sensor located inside a housing of said extracorporealblood treatment machine.
 42. A method as in claim 40, wherein saidpresence is detected by guiding and concentrating a leaking flow ofblood toward a fluid sensor.
 43. A device for detecting a fluid leakfrom a fluid processing machine, comprising the steps of: an airdetection sensor located to detect infiltration of air into a fluidcircuit of said fluid processing machine; a fluid detector located todetect a leakage of fluid from said fluid circuit; an alarm connected tosaid sensor and said fluid detector and configured to output an alarmsignal responsively to signals therefrom.
 44. A device as in claim 43,wherein said alarm is adapted to output said alarm signal when eithersaid sensor or said fluid detector indicates a leak.
 45. A device as inclaim 43, wherein said sensor is located to detect infiltration into afirst part of said fluid circuit and said fluid detector is located todetect fluid from a second part of said fluid circuit, said first andsecond parts having separate respective portions.
 46. A device as inclaim 43, further comprising a mechanism adapted to generate a negativepressure in said fluid circuit to cause air to infiltrate into a breachin said fluid circuit.
 47. A device as in claim 46, wherein saidmechanism is adapted to reverse a direction of flow of fluid in saidfluid circuit.
 48. A device as in claim 43, wherein said fluid circuitis a blood circuit.
 49. A device as in claim 43, wherein said fluidprocessing machine is an extracorporeal blood processing machine.
 50. Adevice for detecting a leak from a blood circuit of an extracorporealblood treatment machine, comprising the steps of: respective detectorslocated to detect leaks of blood from respective portions of a bloodcircuit; at least two of said respective detectors including sensorsconfigured to detect different physical effects correlated with one ormore blood leaks; said respective portions including parts that arenon-overlapping.
 51. A device as in claim 50, further comprising anoutput device connected to receive signals from said respectivedetectors and to output a signal responsively thereto.
 52. A device asin claim 51, further comprising at least one of a fluid line clamp, apump, and an actuator of a flow controller, connected to be controlledby said output device responsively to said signal.
 53. A device as inclaim 51, further comprising an alarm connected to be triggered by saidsignal.
 54. A device as in claim 50, wherein said different physicaleffects include the infiltration of air into a blood circuit and thepresence of blood outside said blood circuit.
 55. A device as in claim54, further comprising an alarm connected to receive signals from saidrespective detectors and to output a signal responsively thereto.
 56. Adevice as in claim 54, further comprising an output device connected toreceive signals from said respective detectors and to output a signalresponsively thereto and at least one of a fluid line clamp, a pump, andan actuator of a flow controller, connected to be controlled by saidoutput device responsively to said signal.
 57. A device as in claim 54,further comprising an output device connected to receive signals fromsaid respective detectors and to output a signal responsively theretoand an alarm connected to generate an output responsively to saidsignal.
 58. A device as in claim 57, wherein said output device anddetectors are configured such that said signal indicates a leak ifeither of either of said respective different physical effects indicatesa leak.
 59. A device as in claim 58, wherein said different physicaleffects include the infiltration of air into a blood circuit and thepresence of blood outside said blood circuit.
 60. A device as in claim59, wherein at least one of said detectors includes an air sensor and amechanism adapted to periodically generate a negative pressure in saidblood circuit such that air infiltrates said blood circuit through anyopenings therein.
 61. A device as in claim 60, wherein said mechanismincludes a mechanism adapted to reverse flow.
 62. A device as in claim50, further comprising a reversing valve, said different physicaleffects include the infiltration of air into said blood circuit causedby periodically reversing a flow of blood in said blood circuit usingsaid reversing valve.
 63. A device as in claim 62, wherein saiddetectors include a fluid sensor located inside a housing of saidextracorporeal blood treatment machine.
 64. A device as in claim 63,further comprising a flow guide adapted to guide and concentrate aleaking flow of blood toward said fluid sensor.